System and method for deconvolution of multiple data tracks

ABSTRACT

A system and method for reading a magnetic medium having a data band thereon, the data band comprising a plurality of simultaneously written data tracks and at least one alignment band. The system in one embodiment includes a plurality of adjacent readers for simultaneously reading the data tracks. At least one reader is also present for reading the at least one alignment band. A mechanism determines a fractional overlap of each reader on the data tracks based on readback of the alignment band. A mechanism extracts data from readback of the data tracks based at least in part on the fractional overlap.

RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. ______to Berman et al., entitled “Tape Head Having Writer Devices and NarrowerRead Devices”, filed concurrently herewith, and which is hereinincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to tape drive heads, and moreparticularly, this invention relates to a write and reader array wherewidths of the readers are smaller than widths of the writers or datatracks.

BACKGROUND OF THE INVENTION

Data is stored on magnetic media such as tape by writing data in amultiplicity of linear tracks. The tracks are separated along thetransverse direction of the tape and a given track runs longitudinallyalong the tape.

In an effort to increase the amount of data that can be written for agiven tape width, efforts have been made to make data tracks adjacent toone another. The most common method for writing is to use writers thatare spaced apart by a predetermined distance. Furthermore, thepredominant method of writing is to have a large separation betweenreaders and a large separation between writers. Adjacent tracks arewritten in separate passes of the tape where the head is stepped over inthe horizontal or transverse direction by the desired track width. Thewriter width is wider than the desired track width. With each pass, thenewly written track overlaps the previously written track so theresulting width of the previous track is the desired final track width.The above described method is termed “shingling”. Another method is towrite adjacent tracks simultaneously. As the separation between tracksbecomes narrower, horizontal motions of the writing/reading headsrelative to the tape will reach values a fraction of the desiredread/write track widths.

The technology used in existing tape storage drives aligns the readerswithin the width of a written track so each reader is aligned over asingle track. The reader is typically smaller than the writer, isaligned therewith, and is reading one single track. This method iscalled “write wide, read narrow.” Because the reader is narrower thanthe writer, the reader will tend not to read adjacent tracks in spite ofthe horizontal “wobble” of the tape relative to the reader as the tapemoves across the head.

FIG. 1 illustrates a typical multitrack tape head 100 having a multitudeof read elements 102 and write elements 104, where the read elements 102are aligned with the write elements 104. Servo elements 106 (one shown)flank the read elements 102 and are used to sense servo tracks on themedium to keep the head 100 aligned over a data track duringreading/writing. The figure shows a “piggy back” structure where awriter is stacked vertically over a paired reader. Many tape heads alsohave readers and writers which are aligned horizontally, either withgroups of readers and groups of writers or alternating readers andwriters.

A major drawback to the traditional “shingling” method, however, is thattape wobble increases the probability of overwriting adjacent datatracks during writing the reverse direction and also causes a randomvariation in the track width along the length of the tape. As the trackwidth decreases, the amount of wobble (or track mis-registration) needsto decrease proportionally. As the track width is decreasing with futuregenerations, it is becoming more difficult to decrease the trackmis-registration sufficiently to keep readers on track and avoid overlapof readers on multiple written tracks.

One approach to control the written tracks is to use adjacent writers soa large group of adjacent tracks will be written simultaneously. Anyhorizontal motion (wobble) during write will cause thesimultaneously-written tracks to move together, so the track-to-trackseparation (pitch) remains fixed within the group. Horizontal motion(wobble) results in large track misregistration during read, as a givenreader can straddle two adjacent written tracks.

Furthermore, the servo tracks used for guiding the head-to-tape-trackalignment are typically written to the tape prior to writing any data.Thus, any wobble of a written track will not be contained in the servotracks. So, during readback, even though the head is following the servotracks, errors occur due to the wobble during both writing and readback.The errors can result in a particular reader reading two or more trackssimultaneously, especially where track spacing is minimal. The resultantsignal is a composition of two fields from both tracks and may makeextraction of the data from any single track impossible.

One approach to solve these problems would be to use a multiplicity ofwriters and readers, where the number of readers is greater than thenumber of writers and to allow for the readers to be misaligned withrespect to the written tracks so that each reader will have componentsof more than one track. The data would then be deconvoluted using analgorithm that took the interference into account. A major difficulty inthe deconvolution is that the group of written tracks will wobble (orwander) in the horizontal location along the length of the tape.

There is accordingly a clearly-felt need in the art for a head assemblyand method for accurately and efficiently deconvoluting a read signalreflecting multiple written data tracks, thereby allowing accuratereading of data in spite of tape wobble. These unresolved problems anddeficiencies are clearly felt in the art and are solved by thisinvention in the manner described below.

SUMMARY OF THE INVENTION

To resolve the aforementioned problems, a system is provided for readinga magnetic medium having a data band thereon, the data band comprising aplurality of simultaneously written data tracks and at least onealignment band. The system in one embodiment includes a plurality ofadjacent readers for simultaneously reading the data tracks. At leastone reader is also present for reading the at least one alignment band.A mechanism determines a fractional overlap of each reader on the datatracks based on readback of the alignment band. Also, a mechanismextracts data from readback of the data tracks based at least in part onthe fractional overlap.

Several methods for determining a fractional overlap of each reader onthe data tracks based on readback of the alignment band and deconvolvingthe data from the data tracks are presented.

Any of these embodiments may be implemented in a tape drive system,which may include a magnetic head including the readers mentioned above,a drive mechanism for passing a magnetic recording tape over themagnetic head, and a controller electrically coupled to the magnetichead.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings.

FIG. 1 is a representative view of a typical multitrack tape head havinga multitude of read and write elements as seen from the tape bearingsurface.

FIG. 2 illustrates a single module portion of a tape head.

FIG. 3 illustrates a head for a read-while-write bidirectional lineartape drive in use, which includes two modules.

FIG. 4 is a representative view of the readers and writers of the moduleof FIG. 2 taken from Circle 4 of FIG. 2 and as seen from the tapebearing surface.

FIG. 5 is a simplified schematic of multiple written tracks, a singleextra written control track, “blank” tracks and multiple readers.

FIG. 6 is a simplified schematic of multiple written tracks on a medium,extra written control tracks on a medium, “blank” tracks on a medium,and multiple readers.

FIG. 7 is a schematic of readers each overlapping two tracks.

FIG. 8 is a schematic of one reader overlapping a single control trackand a blank track.

FIG. 9 is a schematic of one reader over two control tracks.

FIG. 10 is a representative view of an embodiment where the controltracks have angled magnetic transitions.

FIG. 11 is a plot of signal intensity for four parallel written tracksand five read signals overlapping the written tracks versus linear tapedistance.

FIG. 12 is a plot of the four parallel written tracks of FIG. 11 and thecorrected read signals.

FIG. 13 is a plot of two parallel written tracks and three read signalsoverlapping the written tracks versus linear tape distance.

FIG. 14 is a plot of two parallel written tracks of FIG. 13 and thecorrected read signals.

FIG. 15 is a simplified schematic of multiple written tracks, extrawritten tracks, multiple readers, and additional written tracks forcalibration.

FIG. 16 is a schematic illustration of a microtrack profile calibrationprocedure.

FIG. 17 is a schematic illustration of multiple readers which overlapswritten tracks such that an inhomogeneous response is obtained across areader width.

FIG. 18 is a chart illustrating signals generated by an LTO Gen 1 head.

FIG. 19 is a detail of the chart of FIG. 18.

FIGS. 20A-B are charts showing signals generated by an LTO Gen 1 head.

FIGS. 21A-B are charts showing a Fourier transform of signals generatedby an LTO Gen 1 head.

FIG. 22 illustrates a tape drive system according to one embodiment.

FIG. 23 is a representative diagram of readers and written tracks inaccordance with an example.

BEST MODE FOR CARRYING OUT THE INVENTION

The following description is the best embodiment presently contemplatedfor carrying out the present invention. This description is made for thepurpose of illustrating the general principles of the present inventionand is not meant to limit the inventive concepts claimed herein.Further, particular features described herein can be used in combinationwith other described features in each of the various possiblecombinations and permutations.

The following description discloses a method and system for successfullyand accurately reading multiple data tracks where the readers overlapmultiple tracks.

FIG. 2 illustrates a module 200 carrying multiple readers 202 (alsocalled sensors, read elements, etc.) and writers 201 (also called writeelements, etc.). Note FIG. 4, which is a representative view of thereaders and writers of the module of FIG. 2 taken from Circle 4 of FIG.2. As shown, the writers 201 and readers 202 are positioned towards themiddle of the module 200. More description of the readers and writersand preferred configurations will be presented below. One skilled in theart will appreciate that the configuration of write and/or readers 201,202 can vary from those shown without straying from the spirit and scopeof the present invention.

In order to increase the stability of the module 200 for the suitableuse thereof, the module 200 is attached to a beam 206 of some sortformed of a rigid material. Such beams 206 are often referred to as a“U-beam.” A closure 208 is often attached in view of the benefits itaffords in resultant heads.

FIG. 3 illustrates a head 300 for a read-while-write bidirectionallinear tape drive according to one embodiment of the present invention.“Read-while-write” means that the read element follows behind the writeelement. This arrangement allows the data just written by the writeelement to be immediately checked for accuracy and true recording by thefollowing read element.

The head 300 of FIG. 3 is formed by coupling two flat profile modules200, each module including multiple readers and/or writers.Specifically, in FIG. 3, two modules 200 are mounted on U-beams 206which are, in turn, adhesively coupled. Cables 302 are fixedly coupledto the pads. The tape 304 wraps over the modules 200 at a predeterminedwrap angle α. Note that the tape bearing surfaces of the modules 200need not be coplanar, but rather can be angled relative to one anotherto create a desired wrap angle at each facing edge.

It should be noted that the two-module tape head 300 of FIG. 3 isrepresentative only, as the precepts of the present invention can beimplemented in any type of head where multiple tracks of information canbe written and subsequently read.

One skilled in the art will appreciate that the configuration of writeand/or readers 201, 202 can vary. For instance, one module can have allwriters 201, while the other module can have all readers 202. Anotherexample would be to have a plurality of writers 201 and readers 202 allaligned linearly perpendicular to the direction of tape movement. Itshould also be understood that the number of read and writers describedherein are provided by way of example only, and can be increased ordecreased per the desires of the designer, system requirements andcapabilities, etc.

Another variation includes a head having only a single module of readand writers that provides all of the read/write functionality. A secondmodule may or may not be present. Of course the shape of the module maybe different than the module 200 shown in FIG. 2. One skilled in the artwill appreciate how to create a single module design using traditionalhead designs.

FIG. 4 is a representative view of the readers 202 and writers 201 ofthe module 200 according to one embodiment of the present invention. Asshown, the width (W_(R)) of the readers 202 is about the same as thewidth (W_(W)) of the writers 201 and, consequently, the width (W_(T)) ofthe written track 402 (shown in shadow to represent width of data trackon the tape). However, the width (W_(R)) of the readers 202 may begreater or less than the width (W_(W)) of the writers 201 and/or trackwidth (W_(T)) in some embodiments. The spacing between centerpoints ofthe readers 202 are preferably about equal to the spacing betweencenterpoints of the writers 201 as measured in a direction transverse tothe direction of tape travel. Also, note that in many embodiments,including the one shown, more readers 202 are present than writers 201.The importance of these aspects will be discussed in more detail below,and are described here with reference to the drawings to provide contextto the concepts.

As shown, the writers are adjacent to one another, and the readers areadjacent to one another. Adjacent refers to the horizontal alignment.Each reader is horizontally located adjacent to its neighbor with littleor no horizontal separation. The adjacent alignment can also beaccomplished by displacement of neighboring readers in the verticaldirection (direction of tape motion) for physical considerations such asavoiding overlapping leads used to connect the readers to externaldevices, etc. During reading, some readers overlapping two data trackswill generate a convoluted signal reflecting influence from the two datatracks. The read signals representing multiple tracks per reader canthen be deconvoluted to extract the original information written on eachindividual data track. For the following discussion, d represents afractional overlap of a reader over one data track and f represents thefractional overlap of the reader over another data track. If, forexample, read track n (R(n)) has a fraction f of written track n(f*W(n)) and a fraction d of written track n+1(d*W(n+1)), then thevector read signal for readers R is described by the matrix M times thevector written signal W: R=M*W. In the simple case where the readers arehomogeneous, and all readers behave the same, f and d are described byEquations 1 and 2 respectively, below. The diagonal of M is given by f(M(i,i)=f), and the only nonzero components of the off-diagonal elementswould be M(i,i−1)=d. In other words, where the reader is only over onetrack, f will equal 1. Where the reader is overlapping two tracks, thesignal generated by the reader will be dependent upon f and d. Becausein this embodiment of the present invention the reader can only overlaptwo tracks, the only nonzero components of the off-diagonal elementswould be d. If the values of f and d are not known, then the algorithmwill need to determine both f and d to deconvolve the signals R toobtain the written signals W. A major difficulty in the deconvolutionprocess is that the group of written tracks will wobble (or wander) inthe horizontal location along the length of the tape, making the valuesof f and d change along the track length. As described below, thisdifficulty has been overcome by the present invention.

To enable the system to determine the relative position of the readers202 relative to the data tracks (e.g., the overlap of the readersrelative to the tracks) an alignment band is used. The alignment band iswritten concurrently with the data tracks. The alignment band caninclude one or more written tracks of a known pattern (control track(s))on the medium. The alignment band can also merely be on one or moreerase or “blank” tracks. Suggested alignment signals are describedbelow, and generally include a combination of “blank” tracks and controltracks.

FIG. 5 illustrates a data band including multiple written tracksW(1)-W(4), an extra written track (control track) WE(1), and erase or“blank” tracks Wb(1), Wb(2) sandwiching (surrounding or flanking) thecontrol track WE(1). Note that the tracks W(1)-W(4), WE(1), Wb(1), andWb(2) may be spaced from one another, may be immediately adjacent to oneanother, may overlap each other, or a combination of these modes. Alsoshown are multiple readers 202 and are identified as RE(1)-RE(4),R(1)-R(5). This example shows a case where blank tracks Wb(1) and Wb(3)are wider than a reader so it can be easily determined where the readersare located. Use of tracks wider than the reader is not necessary if thestandard servo data is used. The outer blank written tracks Wb(1) andWb(3) may also be one track width wide. The example is FIG. 5 representsthe minimum suggested number of blank and extra tracks.

FIG. 6 illustrates multiple written tracks W(1)-W(4), extra writtencontrol tracks WE(1), WE(2), “blank” tracks Wb(1)-Wb(4) and multiplereaders 202. It should be noted that the space between tracks is only tomake it easier for the reader to see the separation, and need not bepresent. This figure shows four blank written tracks Wb(1)-Wb(4) and twocontrol tracks WE(1), WE(2) sandwiched by them, for a total of twoadditional written tracks when compared to the embodiment in FIG. 5.Adding additional control tracks improves the robustness of the schemebut also decreases the density of data tracks on the medium.

As shown in each case of FIG. 5 or FIG. 6 above, the control track(s)is/are separated or isolated from the other written tracks. The controltrack or tracks can be isolated, for example, by writing a DC ORAC-erased track (blank) on either side of the isolated control track, asshown. It is also preferable to write at least one DC OR AC erased track(blank) on the far side of the written data tracks to isolate the groupof written data tracks. And alternating current (AC) erased track couldalso be used. Then the readers which read the written control track(s)will only pick up a signal from the control track, making thedetermination of f and d unambiguous. The outer DC OR AC erased track(blank) enables a determination of the end of the data track and ensuresthat the outer reader reads only a single data track. The isolatedcontrol track, the DC OR AC erase track and the desired written tracksare preferably all written simultaneously so any wander in the bundle oftracks will be identical for all written tracks. The resulting trackswill be adjacent to one another and have about a constant (though notnecessarily equal) center to center spacing along the length of the bandof tracks.

Because the tracks are always uniformly spaced, the fractional signalsread by the readers overlapping the isolated control track will beidentical to the fraction of signals from readers overlapping any otherwritten tracks, unambiguously allowing determination of the matrixinversion. The width of the outer DC OR AC erase tracks is preferably atleast one track width wide, but might be chosen to be larger dependingon the amount of track misregistration. Complications such as those dueto differences in the response signal of a reader or non-homogeneousresponse along a reader/writer track width can be determined by acalibration procedure and the values stored in a look up table. Theinversion matrix can then be appropriately adjusted.

To illustrate the general method according to one embodiment of thepresent invention, assume N read tracks are on a head and P writtentracks are present, with the width of the read and write tracks beingnearly identical. Also assume N is greater than P, and that the writersare adjacent and the readers are adjacent. The signal for reader track n(R(n)) has a fraction f of written track n (f*W(n)) and a fraction d ofwritten track n+1 (d*W(n+1)). (Assuming the signals have the sameintensity and the readers abut one another, then d=1−f). As mentionedabove, d represents a fractional overlap of a reader over one data trackand f represents the fractional overlap of the reader over another datatrack. FIG. 7 shows a schematic of a system where the fractional overlapd for a particular reader is equal to 1−f. In FIG. 7, a first readerR(1) overlaps a DC OR AC erased (blank) track Wb(2) and written trackW(1) respectively by fractions f and d, while reader R(2) overlapswritten tracks W(1) and W(2) with respective overlaps of d and f. Theoverlaps f and d can be calculated according to the following formulae,where x is the length of overlap of the reader over one track, y is thelength of overlap of the reader over another track, and W_(R) is thetotal width of the reader, as shown in FIG. 7.f=x/W _(R)  Equation 1d=y/W _(R)=1−f  Equation 2

The vector signal R for the readers is described by the matrix M timesthe vector signal W: R=M*W. The diagonal of M is given by f (M(i,i)=f),and the only nonzero components of the off-diagonal elements would beM(i,i−1)=d. If the values of f and d are not known, then the algorithmwill need to determine both f and d to deconvolve the signals R toobtain the written signals W. A major difficulty in prior methods ofdeconvolution was that the group of written tracks will wobble (orwander) in the horizontal location along the length of the tape, makingthe values of f and d change along the track length. The writers used towrite the tracks in this method of the present invention are alignedadjacent to one another and all tracks are written simultaneously so anywander in the bundle of tracks will be identical for all written tracks.The resulting tracks will be adjacent to one another and have about aconstant (though not necessarily equal) center to center spacing alongthe length of the band of tracks.

For simplicity, and to match the illustrations in FIGS. 5-6, fourwritten tracks W(1)-W(4) and five read tracks R(1)-R(5) are considered.Reader R(1) covers a fraction f of written track W(1), and reader R(2)covers a fraction f of track W(2) and d of track W(1). Taking R and W tobe vectors where R is the read signal and W is the written signal, thematrix describing the signals is: $M\quad = \begin{matrix}{\quad\left\lbrack \quad{f,\quad 0,\quad 0,\quad 0,\quad 0} \right\rbrack} \\{\quad\left\lbrack \quad{d\quad,\quad f,\quad 0,\quad 0,\quad 0} \right\rbrack} \\\left\lbrack \quad{0,\quad d,\quad f,\quad 0,\quad 0} \right\rbrack \\\left\lbrack \quad{0,\quad 0,\quad d,\quad f,\quad 0} \right\rbrack \\\left\lbrack \quad{0,\quad 0,\quad 0,\quad d,\quad f}\quad \right\rbrack\end{matrix}$The inverse of matrix M is: ${IM} = \begin{matrix}\begin{bmatrix}{{1/f},} & {0,} & {0,} & {0,} & 0\end{bmatrix} \\\left\lbrack \quad\begin{matrix}{{{{- 1}/{f\hat{}2}}*d},} & {{1/f},} & {0,} & {0,} & 0\end{matrix} \right\rbrack \\\left\lbrack \quad\begin{matrix}{{{d\hat{}2}/{f\hat{}3}},} & {{{{- 1}/{f\hat{}2}}*d},} & {{1/f},} & {0,} & 0\end{matrix} \right\rbrack \\\begin{bmatrix}{{{- {d\hat{}3}}/{f\hat{}4}},} & {{{d\hat{}2}/{f\hat{}3}},} & {{{{- 1}/{f\hat{}2}}*d},} & {{1/f},} & 0\end{bmatrix} \\\begin{bmatrix}{{{d\hat{}4}/{f\hat{}5}},} & {{{d\hat{}2}/{f\hat{}3}},} & {{{{- 1}/{f\hat{}2}}*d},} & {{1/f},} & 0\end{bmatrix}\end{matrix}$The written track vector is: W=(W(1), W(2), W(3), W(4), 0)while the read vector is: R=(R(1), R(2), R(3), R(4), R(5)).

The general solution to the inversion matrix for the number of writtentracks being Ntrack requires a matrix dimension of Ndim=Ntrack+1, andassuming equal amplitude response for all readers and a uniform responsealong each reader track width.MI(1:Ndim,1:Ndim)=0;

for jr=1:Ndim

-   -   for jc=1:jr        MI(jr,jc)=((−1)ˆ(jc+jr))*((1/f){acute over (        )}(1+Ndim−jc))*(dˆ(Ndim−jc));    -   end

end

The read signal given the written signal will be:R=M*W  Equation 3

The deconvolved written tracks (DW) are given by:DW=IM*R=IM*M*W  Equation 4

An equally valid matrix is: ${M\quad 2} = \begin{matrix}\left\lbrack {d,\quad f,\quad 0,\quad 0,\quad 0,\quad 0} \right\rbrack \\\left\lbrack {0,\quad d,\quad f,\quad 0,\quad 0,\quad 0} \right\rbrack \\\left\lbrack \quad{0,\quad 0,\quad d,\quad f,\quad 0}\quad \right\rbrack \\\left\lbrack \quad{0,0,\quad 0,\quad d,\quad f} \right\rbrack \\\left\lbrack \quad{0,0,\quad 0\quad,\quad 0\quad,\quad d}\quad \right\rbrack\end{matrix}$The inverse of matrix M2 is: ${{IM}\quad 2} = \begin{matrix}\begin{bmatrix}{{1/d},} & {{{- f}/{d\hat{}2}},} & {{{f\hat{}2}/{d\hat{}3}},} & {{{- {f\hat{}3}}/{d\hat{}4}},} & {{f\hat{}4}/{d\hat{}5}}\end{bmatrix} \\\begin{bmatrix}{0,} & {{1/d},} & {{{- f}/{d\hat{}2}},} & {{{f\hat{}2}/{d\hat{}3}},} & {{- {f\hat{}3}}/{d\hat{}4}}\end{bmatrix} \\\left\lbrack \begin{matrix}{0,} & {0,} & {{1/d},} & {{{- f}/{d\hat{}2}},} & {{{f\hat{}2}/{d\hat{}3}}\quad}\end{matrix}\quad \right\rbrack \\\left\lbrack \quad\begin{matrix}{0,} & {0,} & {0,} & {{1/d},} & {{- f}/{d\hat{}2}}\end{matrix} \right\rbrack \\\begin{bmatrix}{0,} & {0,} & {0,} & 0 & {1/d}\end{bmatrix}\end{matrix}$The written track vector is: W2=(0, W(1), W(2), W(3), W(4))while the read vector is: R2=(R(1), R(2), R(3), R(4), R(5)).

This second matrix (IM2) would be a better choice when d>f, especiallywhen f<<1, due to errors in the signal to noise ratio (SNR) and the 1/ffactors. The first matrix (IM) would be better when f>d. The two canalso be combined to offer better SNR.

If an additional, isolated written track(s) WE(j) are madesimultaneously (assuming at least one additional “extra” control trackis written, surrounded by “blank” zones), the horizontal motion of theextra track(s) will be identical to that of the tracks with the “random”information written on the data tracks W. Since the extra track(s) isisolated (due to the “blank” zones, e.g., DC OR AC erased), the readerreading that signal will only get the signal from that track. With oneextra control track (WE(1)), the values of f and d can be determined byEquations 5 and 6 (refer also to FIG. 7).f=x/W _(R) =RE(1)/[RE(1)+RE(2)]  Equation 5d=y/W _(R)=1−f=RE(2)/[RE(1)+RE(2)]  Equation 6

When the width of the readers is less than the width of the writers so aspacing exists between readers, f and d are still given by the above twoequations.

“Dead” regions (e.g., drop out zones) on the tape might occur where theextra written track is not written, so having an extra written track oneither end of the group of data tracks might be desired and would givethe user more flexibility in determining the relative off-trackcoupling.

For a tape to which no data has been written, the “blank” zone regionswill inherently exist simply by not writing data over that region. Oncea tape has been written to, transverse motion of the tape with respectto the head results in a variation in the location of the “blank” zoneregion for different passes over the same region of the tape. This maynecessitate the creation of a “blank” zone whenever the tape is writtento. This can be accomplished by having writers over the “blank” zoneregions erase the tape in the “blank” zone simultaneously to data beingwritten (Wb(1)-Wb(3)). This will ensure that the “blank” zones exist andfollow the “wobble” of the written data tracks. An example of a tapeerasure would be a “DC” erasure performed by writers over tracksWb(1)-Wb(4) being powered with a constant current throughout the entirewrite process, sufficient to magnetizing the tape in the “blank zoneregions in one orientation without any transitions. An “AC” erasuregenerally refers to applying a sufficiently high frequency current tothe writers at a sufficiently high current level to write alternatelyoriented magnetic transitions on the tape at a physical spacing smallenough that the read heads could not read them.

Servos and servo tracks may be used to maintain track following (and maybe considered “control” tracks), but extra written control track(s)along with the “blank” zones will greatly assist in deconvoluting thesignals due to overlap of the different written tracks onto each reader.The extra written tracks can also serve as a fine tune servo signal. Theinversion matrix (IM) is uniquely determined with only the knowledge off and d. Application of the inversion matrix is a simple summation andmultiplication. While the extra written tracks and the “blank zone”separating the extra written tracks from the data tracks uses storagespace, with a large number of simultaneously written tracks (16, 32, 64,. . . ) the fractional loss of area diminishes.

Several methods for determining the overlap of a reader or readerrelative to a control track or tracks are presented below. Each of thesemethods assumes that the control tracks are written simultaneously towriting the data tracks so the track to track spacing in a particulardata band will be constant in spite of any wobble. In other words, thewobble in the control track(s) and the wobble in the data tracks will beidentical. In any of the following embodiments, one or more controltracks are written simultaneously with the data tracks.

In a single control track embodiment, as shown in FIG. 8, the controltrack WE(1) can be written adjacent to a DC or AC erased track Wb(1) andoptionally Wb(2). The control track is then read back with a singlereader RE(1). Preferably, the control track signal is a sinusoid. Thereader signal amplitude is proportional to the amount of overlap of thereader on the control track. If the reader is completely over thecontrol track, the readback signal will be at a maximum value. When thereader is 50% over the control track, the readback signal will be at 50%of the maximum value.

It should be kept in mind that noise will always be present. And becausethis method uses the amplitude of the readback signal to determine therelative overlap of the reader, changes in the amplitude may or may notindicate a true position. The amplitude can be affected by a variety ofthings, not just head position. For instance, even if the reader is onthe track exactly, the amplitude will still vary from such things ashead-tape spacing, grain magnetization, variation in magnetic graindensity, tape defects, randomness of particles in the erase band, etc.

To provide even more reliability, one embodiment uses multiple headsreading the same control track. For example, two readers can be used toread a single control track that is surrounded by two erase tracks, asin FIG. 7. Here, the difference in the amplitudes of the two readers canbe used to generate the position information. A decrease in amplitude inone head should correlate to an increase in amplitude in the other head,and so the relative positions of the readers to the control track can becalculated based on the proportional signal from each head. Any loss inamplitude across both readers may indicate a variation due to head-tapespacing, grain magnetization, variation in magnetic grain density, tapedefects, etc. rather than a change of position relative to the controltrack.

In another embodiment, shown in FIG. 9, two adjacent control tracksWE(1), WE(2) can be read back with a single reader RE(1). The twocontrol tracks are written with different patterns. For example, twosinusoids can be used with slightly different frequencies (preferablynot harmonics). The single reader generates signals from both controltracks. The resultant combined signal can be then be separated byfiltering in a manner known in the art. The position information isobtained by measuring the relative amplitudes of the two components inthe frequency domain and compared to a nominal value that compensatesfor the Wallace frequency dependence of the head. Based on theproportional strength of the amplitudes relative to each other, theposition of the reader can be determined. This embodiment may eliminateany problems that would otherwise be caused by noise from an erase band.

In a further embodiment, two (or more) pseudo-random bit sequences(PRBS) can be chosen instead of two sinusoids to be written on dualcontrol tracks (adjacent or separated, one or more readers per controltrack). The PRBS sequences should be orthogonal to each other androtated versions of each other. The reader signal on these two tracksmay be output to two matched filters, matched to the two PRBS sequences.The ratio of the outputs of the two matched filters can be used forpositioning information. This is different than the previous method,because now simple sinusoids are not merely written, but ratherrepeating, random-appearing patterns are present in the control tracks.

It is important that the two PRBS sequences are unique enough to beidentified. For instance, they may be orthogonal. This means that thedot product of the two sequences is zero or very small. If one of thesequences is rotated by an arbitrary number of bits, meaning that anumber of bits from the end of the sequence are appended to thebeginning, the dot product of the rotated sequences should be very smallas well.

Consider the following example. Control track 1 has a pseudo-random bitsequence and control track 2 has a different pseudo-random bit sequence.The bit sequences can cover the entire frequency domain, and preferablyare optimized for a high signal to noise ratio. So from the frequencydomain, the signals may be nearly indistinguishable. Accordingly, theserving is performed in the time domain. The same sequences repeat overand over in each control track. A matched filter recognizes a match inthe pseudo-random bit sequence, its output goes high thereby indicatinga match. A second matched filter similarly analyzes the second controltrack.

In another embodiment, two control tracks are written on either side ofthe adjacent track bundle having an erase track on both sides, as inFIG. 6. The control tracks can be read back with two readers. Theposition information is generated from the amplitude difference betweenthe two head outputs.

In yet another embodiment, control tracks also provide timing and phaseinformation for clock recovery for the data read channels. As is wellknown in the art, the readback system of a storage system deciphers ordecodes an incoming readback signal into 1s ands 0s, thereby translatingthe signal into bits that were written to the tape (read channel). Theclock recovery subsystem synchronizes the clock of the readback systemto the clock of the write system so the drive knows when 1s and 0s arecoming in on the readback signal. Clock recovery is one of the mostdifficult processes in tape drive readback systems. Particularly, anyloss of signal or dropout can cause the drive to lose the clock.Accordingly, any way to improve clock recovery is desirable.

Error correction is typically built in. However, all of this isdownstream from the initial data read. So if the timing is lost, theeffects are not known immediately and large errors are typical. So itwould be desirable to ensure that the clock is properly aligned to thetiming signal, as well as detect timing errors more quickly.

To assist in timing verification, the control tracks can providefrequency and phase information for the clock recovery circuits in thedata read channels. A sinusoid signal of known period is preferred as itis periodic in nature, and so the velocity of the tape and thus thetiming can be easily calculated.

In a further embodiment, positioning information is obtained from thephase difference of two readers RE(1), RE(3) on two control tracksWE(1), WE(2) with angled magnetic transitions. Note that additionalreaders RE(2), RE(4) may be provided to add robustness. The anglebetween the transitions tilt so that the two tracks provides phase-basedposition information as shown in FIG. 10.

Each reader is preferably smaller than the width of the associatedcontrol track. As the medium passes by the readers, a pulse is generatedat each written transition on the medium. When the two heads are in themiddle, of the respective control tracks, the pulses arrive together. Ifthe readers move laterally, one reader's pulse arrives sooner and theother reader's pulse arrives later. By measuring the spacing of thepulses, the positions of the readers relative to the control tracks canbe determined.

To write the angled transitions, the writers are set at an angle.

FIGS. 11 and 12 show an example of the process using mathematicallygenerated signals. Again, it is assumed that the overlap is determinedby reading the signals from control tracks WE(1) and/or WE(2) usingreaders RE(1) and RE(2) and/or RE(3) and RE(4).

FIG. 11 is a plot of four parallel written tracks (symbol) and five readsignals (line). FIG. 12 is a plot of four parallel written tracks(symbol) and the corrected read signals (line). In both FIGS. 11 and 12,the written tracks are all of the same amplitude, but out of phase bypi/2. The five read tracks are shifted horizontally with respect to thewritten tracks by 30% of the track width so the first read track has 70%of the first written track. The second read track has 30% of the firstwritten track and 70% of the second written track, etc.

FIG. 13 shows an example of the process using two adjacent trackswritten on to tape and read from the tape from an LTO drive (symbol).The second track is purposefully offset in time from the first toaccentuate the effect of overlap. The three read tracks (indicated bylines) are shifted horizontally with respect to the written tracks by50% of the track width so the first read track has 50% of the firstwritten track. The second read track has 50% of the first written trackand 50% of the second written track. The third read track has 50% of thesecond written track. FIG. 14 shows the deconvolution of the readoverlapped signals of FIG. 13, illustrating recovery of the originaltracks. The inversion matrix assumes that the 50% overlap is known.

The matrices described for the read signals (M) and the de-convolutionof the read signals (MI) assumes that all of the readers have the sameresponse. If the response of each reader is different, then a morecomplicated deconvolution algorithm may be implemented. Potentialnon-linearity or nonuniformity differences between readers include: (a)magnitude (amplitude); (b) asymmetry between positive and negativeresponse; (c) differences in frequency response.

Regarding magnitude (amplitude) differences, magnitude or amplitudecorrections are relatively easy to perform as long as they do not varywith time. Amplitude variations between the different readers due totheir inherent differences in response are given by the matrix MA:MA(i,i)=A(i)  Equation 7andMA(i,j)=0  Equation 8when j≠i.The inversion matrix (IMA) is:IMA(i,i)=1/A(i)  Equation 9andIMA(i,j)=0  Equation 10when j≠i.Regarding asymmetry differences, matrices similar to MA and IMA describeasymmetric reader responses, but two values of A(i) are used:A(i)=Ap(i)  Equation 11if R(i)>0, andA(i)=An(i)  Equation 12if R(i)<0.

In order to utilize the more complicated correction algorithms, theresponse of the readers must be determined. One method of determiningthe response of the readers is to calibrate them in a designated sectionof the tape. In the calibration section of the tape, all writers writethe same pattern. The amplitude and asymmetry response of each readercan then be determined. Even the frequency response can be determined.It is best if the frequency response of the readers is compensated forin the hardware such as the methods employed in existing tape drivesusing equalizer filters to boost high frequency signals, etc. To be surethat the edge readers are calibrated properly, more writers than thosewriting data should be employed. FIG. 15 shows a scheme to calibratereader amplitude and asymmetries. In FIG. 15, enough written tracks areused so the written pattern extends beyond all of the readers. In apreferred embodiment, one writer is associated with one reader with anadditional writer used to write tracks on either end of the array (i.e.,the number of writers is two greater than the number of readers beingcalibrated).

Conversion of the read signals into data bits can be accomplished usingstandard algorithms such as peak detect or partial response, maximumlikelihood (PRML), but would be applied to the corrected read signals(CR) rather than the directly read signals (R).

A method of resolving a non-homogeneous reader profile along the readertrack width is to perform an in-drive microtrack profile calibration.FIG. 16 is a schematic example of a certain embodiment, where datatracks, such as W(1), W(3), W(5), W(7), are written with a specificpattern using alternate writers along a segment of tape. The head isthen passed over the calibration region, intentionally shifting theheads horizontally and measuring the signals as the tape is runlongitudinally. In FIG. 16, the tape is moving vertically and the headis being moved from left to right as shown progressively in rows 16(a)to 16(d). The recorded signal for the odd readers R(1) will go from zerosignal in 16(a) to a small number in 16(b) to maximum signal in 16(c) tozero in 16(d). The response of all readers along their track width willthen be known, and can be factored into the matrix manipulation.

FIG. 17 depicts the situation for a non-homogeneous response across areader width. Each reader has a different response. f(n,x) is theresponse of the nth reader from 0 to x and d(n,x) is the response of thenth reader from x to W_(R). The values of f(n,x) and d(n,x) are measuredduring the calibration procedure as shown in FIG. 13, where alternatetracks are written and the head is stepped horizontally while the tapeis moving vertically. The values of f(n,x) and d(n,x) are then stored ina look-up table. The matrix (M) and inversion matrix (IM) for fourwritten tracks with a five reader array is: $M = \begin{matrix}\left\lbrack {{f\quad 1},0,0,0,0} \right\rbrack \\\left\lbrack {{d\quad 2},{f\quad 2},0,0,0} \right\rbrack \\\left\lbrack {0,{d\quad 3},{f\quad 3},0,0} \right\rbrack \\\left\lbrack {0,0,{d\quad 4},{f\quad 4},0} \right\rbrack \\\left\lbrack {0,0,0,{d\quad 5},{f\quad 5}} \right\rbrack\end{matrix}$ ${IM} = \begin{matrix}\begin{bmatrix}{{{1/f}\quad 1},} & {0,} & {0,} & {0,} & 0\end{bmatrix} \\\begin{bmatrix}{{{{- d}\quad{{2/Q}/f}\quad 1},}\quad} & {{{{1/f}\quad 2},}\quad} & {{0,}\quad} & {{0,}\quad} & 0\end{bmatrix} \\\begin{bmatrix}{d\quad 3*d\quad{2/f}\quad{3/f}\quad{2/f}\quad 1} & {{{{- d}\quad{3/f}\quad{3/f}\quad 2},}\quad} & {{{{1/f}\quad 3},}\quad} & {{0,}\quad} & 0\end{bmatrix} \\\begin{bmatrix}{{{- d}\quad 4*d\quad 3*d\quad{2/f}\quad{4/f}\quad{3/f}\quad{2/f}\quad 1},} & {d\quad 3*d\quad{2/f}\quad{3/f}\quad{2/f}\quad 1} & {{{- d}\quad{3/f}\quad{3/f}\quad 2},} & {{{{1/f}\quad 3},}\quad} & 0\end{bmatrix} \\{\begin{bmatrix}{{0,}\quad} & {{0,}\quad} & {{0,}\quad} & {{0,}\quad} & {{1/d}\quad 5}\end{bmatrix}.}\end{matrix}$

Such that ${{{IM}*M} + I} = \begin{matrix}\begin{bmatrix}{1,} & {0,} & {0,} & {0,} & 0\end{bmatrix} \\\begin{bmatrix}{0,} & {1,} & {0,} & {0,} & 0\end{bmatrix} \\\begin{bmatrix}{0,} & {0,} & {1,} & {0,} & 0\end{bmatrix} \\\begin{bmatrix}{0,} & {0,} & {0,} & {1,} & 0\end{bmatrix} \\\begin{bmatrix}{0,} & {0,} & {0,} & {0,} & 1\end{bmatrix}\end{matrix}$

where I is the identity matrix or the diagonal matrix.

The value of fn (=f(n,x)) and dn (=d(n,x)) are a function of x. Thefunction of x has been left out of the matrix for simplicity. The valueof x is determined by the “extra” (control) written track(s) by thecontinuously measured vales of fE (=fE(x)) and dE (=dE(x)), where thevalues of ffi and dn are predetermined. For actual use, the track can bedivided into segments and the appropriate inversion matrices can bestored in a look-up table.

The value of f(j) and d(j) used in IM to deconvolute the signal is madeby the measurement of fE and dE from the “extra” (control) track(s). Forexample, if all tracks have uniform response across their width, thenfE=(x/WR), and dE=1−fE so all f(jr)=fE and all d(jr)=dE.

For a better determination of fE(x) and dE(x), rather than just relyingon instantaneous values, an appropriate integral using an appropriatetime can be used. The general form of the matrix is:

ndim=length(f);

for jr=1:ndim, for jc=1:ndim, M(jr,jc)=0; end, end

M(1,1)=f(1); for jr=2:ndim, M(jr,jr)=for); M(jr,jr−1)=d(jr); end

The general form of the inversion matrix is:

for jr=1:ndim, for jc=1:ndim, M(jr,jc)=0; end, end

MI(1,1)=1/f(1);

for jr=2:ndim

jc=jr; MI(jr,jc)=1/f(jr);

for nc=2:jr, jc=jc−1; IM(jr,jc)=−1*(d(jc+1)/f(jc))*MI(jr,jc+1); end

end

The read signal given the written signal will be:R=M*W  Equation 13The deconvoluted written (DW) tracks is given by:DW=IM*R=IM*(M*W)=(IM*M)*W=I*W=W  Equation 14Test of Superposition Using a Real Head

As a check that the response of the readers is linear so that thesignals from readers which overlap two written tracks can be deconvolvedusing superposition, an experiment was tried with an LTO Generation 1(Gen 1) head. This experiment provides a first indication of thefeasibility of the deconvolution techniques described herein. The LTOGen 1 heads have S_(R)=S_(W)=333 μm, W_(R)=12.6 μm and W_(W)=26.5 μm.The LTO Gen 1 heads have 8 readers and 8 writers on two modules. Thereaders of the “reading” module are aligned with the writers of the“writing” module. In the experiment, the tape was first AC erased. An 8Tpattern was then written for a section of tape tracks W1(8T), W2(8T), .. . W8(8T) are all separated transversely by 333 μm.

FIG. 18 illustrates signals generated by an LTO Gen 1 head configured asdescribed above. Reader R1 is aligned on written track W1 (8T), whilereader R2 is positioned at ˜50% on written track W2(8T) and −50% ontrack W1(2T). 2T and 8T refer to the patterns. An 8T pattern is written.The head was shifted by 333+20 μm so W1(8T) is an isolated 8T patternand W1(2T) overlaps W2(8T). The overlap is ˜6.8 μm (20 μ-W_(W)/2) fromthe center of the 8T pattern. The head was then located so R2 iscentered on the overlap of W2(8T) and W1(2T). The overlap of R1 withW1(8T) is ˜98%. Prior to about data point 780, the signal from R1 isjust noise while R2 is a 2T pattern due to the starting point of the 2Tpattern being earlier than the 8T pattern starting point.

The top curve of FIG. 18 shows the response of Reader R1 centered ontrack W1(8T). The flat line prior to channel ˜780 is simply AC erasednoise. The transitions seen from channel ˜780 to 1000 are the 8Tpattern. The head is then moved by 333+20 μm and a 2T pattern is thenwritten. With this step, tracks W1(8T) and W8(2T) are isolated. TracksWn+1(8T) are adjacent to tracks Wn(2T) (n=1:7) with Wn+1(8T) beingnominally 20 μm wide and Wn(2T) being the full 26.5 μm wide. FIG. 20Ashows the response of reader R2 centered on track W2(2T) as a clean 2Tpattern. The head is then moved to position 6.8 μm so R1 is nominally98% on W1(8T) and R2 is nominally 50% on W2(8T) and W1(2T). The lowertrace in FIG. 18 shows the resulting signal for R2. Between channel 0and ˜780 a 2T pattern is read, which is the pattern from −50%*W1(2T). Atchannel ˜780, the 8T pattern from W2(8T) is also picked up yielding amixed signal of ˜50%*W1(8T) plus ˜50%*W1(2T).

FIG. 19 is a blow up of FIG. 18 starting at channel 780 where both theR1 and R2 signals are shifted to the average of the preceding data.Particularly, the R1, 8T pattern and R2, mixed 8T and 2T patterns areshown. Only the first few 8T flux reversals are shown.

The best attempt to deconvolute the mixed signal is shown in FIG. 20B,which shows the reader R2 deconvoluted 2T pattern where the isolated 8Tpattern read simultaneously with R1 on W1(8T) is subtracted from themixed signal of R2 which was situated ˜50% on written track W2(8T) and˜50% on W1(2T). FIG. 20B is equal to R2′(2T′)=R2(8T,2T)−0.43*R1(8T) or43% of the signal from R1(8T) is subtracted from R2(2T,8T). FIG. 21A isa Fourier transform of R1(8T), R2(2T), the mixed signal R2(8T,2T) thedeconvolution of the mixed signal R2, (R2, deconvoluted(2T) orR2′(2T′)). The frequency content of the mixed signal R2(8T,2T) is a sumof the frequency contents of the “clean” 8T and the 2T patterns. Thefrequency content of the deconvoluted signal R2′(2T′) is predominantlythat of the 2T pattern, as seen in FIG. 21B where the fraction of theFourier amplitude for the 8T pattern is <2% of the Fourier amplitude ofthe 2T pattern. Going back to time-base signals (FIGS. 20A-20B) thevariation in the amplitude of R2′(2T′) is larger than that of 2T patternfor R2(2T). The reason for the larger amplitude variation in R2′(2T′)than R2(2T) include: (a) the 8T pattern from R1(8T) is slightly out ofphase in time with R2(8T); (b) the spatial amplitude variation forR1(8T) is different from the content of the 8T pattern in R2(8T,2T); (c)the transverse motion of the tape during the measurement of R2(8T,2T)can not be compensated for with the extant LTO Gen 1 heads. Concept (c)is a major factor in the variation of the amplitudes for R2′(2T1). Witha 50% overlap, nominally 6.3 μm of R2 is over W2(8T) and 6.3 μm is overW2(2T). If the tape wanders +/−0.5 μm during the span of 2.5 μs (250channels, 10 ns/channel), then the fraction of W1(8T) will vary from 46to 54%. With these experimental limitations, the deconvolution shown inthe FIGS. yields proof of concept.

FIG. 22 illustrates a tape drive which may be employed in the context ofthe various aspects of the present invention. While one specificimplementation of a tape drive is shown in FIG. 22, it should be notedthat the embodiments of the previous figures may be implemented in thecontext of any type of drive (i.e. hard drive, tape drive, etc.)

As shown, a tape supply cartridge 2220 and a take-up reel 2221 areprovided to support a tape 2222. These may form part of a removablecassette and are not necessarily part of the system. Guides 2225 guidethe tape 2222 across a bidirectional tape head 2226. Such bidirectionaltape head 2226 is in turn coupled to a controller assembly 2228 via acompression-type MR connector cable 2230. The actuator 2232 controlsposition of the head 2226 relative to the tape 2222.

A tape drive, such as that illustrated in FIG. 22, includes drivemotor(s) to drive the tape supply cartridge 2220 and the take-up reel2221 to move the tape 2222 linearly over the head 2226. The tape drivealso includes a read/write channel to transmit data to the head 2226 tobe recorded on the tape 2222 and to receive data read by the head 2226from the tape 2222. An interface is also provided for communicationbetween the tape drive and a host (integral or external) to send andreceive the data and for controlling the operation of the tape drive andcommunicating the status of the tape drive to the host, all asunderstood by those of skill in the art.

The controller 2228 may perform any of the functionality described aboveincluding calculation of overlap, inverse matrix calculation, datarecovery, etc. Alternatively, a host system may receive signals from thehead (via any path) and perform the deconvolution. In a furtheralternative, the controller and host share duties. The controller and/orhost may each contain mechanisms (e.g., logic, software modules,processors, etc.) to perform any function described herein.

EXAMPLE

FIG. 23 illustrates an example of how to calculate an overlap of readerson tracks. In the illustration seven readers 202 overlie five writtentracks. Tracks 1 and 5 are alignment bands. Assume that tracks 1 and 5have twice the track width (TW) as tracks 2-4, which allows the readerarray to move within the data band. The reader width (RW) is not equalto the track width, but rather satisfies the following equation:TW=aRW  Equation 15

The head boundaries are indicated on FIG. 23 as hb0-hb7. The headboundary locations are determined by the following equation:hb _(i) =i−1−e/RW, for i=0 to 7  Equation 16Head equations assume linear inter-track interference. Each head signalis a linear combination of track signals:h1=t1  Equation 17h2=abs(hb1)*t1+hb2*t2  Equation 18h3=(a−hb2)*t2+(hb3−a)*t3  Equation 19h4=t3  Equation 20h5=(2a−hb4)*t3+(hb5−2a)*t4  Equation 21h6=(3a−hb5)*t4+(hb6−3a)*t5  Equation 22h7=t5  Equation 23Here, assume a=1.3 and e/RW=0.5. The resulting head boundary positionsare calculated as:hb1=−0.5, hb2=0.5, hb3=1.5, hb4=2.5, hb5=3.5, hb6=4.5

Plugging this information into Equations 17-23: Track equations: Headequations: [add head equations with same track] h1 = t1 h2 = 0.5*t1 +0.5*t2 1.5*t1 + 0.5*t2 = h1 + h2 h3 = 0.8*t2 + 0.2*t3 0.5*t1 + 1.3*t2 +0.2*t3 = h2 + h3 h4 = t3 0.8*t2 + 1.3*t3 + 0.9*t4 = h3 + h4 + h5 h5 =0.1*t3 + 0.9*t4 0.1*t3 + 1.3*t4 + 0.6*t5 = h5 + h6 h6 = 0.4*t4 + 0.6*t50.4*t4 + 1.6*t5 = h6 + h7 h7 = t5

The matrix form of the equations is: $\begin{matrix}\left\lbrack {t\quad 1} \right\rbrack \\\left\lbrack {t\quad 2} \right\rbrack \\\left\lbrack {t\quad 3} \right\rbrack \\\left\lbrack {t\quad 4} \right\rbrack \\\left\lbrack {t\quad 5} \right\rbrack\end{matrix}\begin{matrix}\begin{bmatrix}1.5 & 0.5 & 0 & 0 & 0\end{bmatrix}^{- 1} \\\begin{bmatrix}0.5 & 1.3 & 0.2 & 0 & 0\end{bmatrix} \\\begin{bmatrix}0 & 0.8 & 1.3 & 0.9 & 0\end{bmatrix} \\\begin{bmatrix}0 & 0 & 0.1 & 1.3 & 0.6\end{bmatrix} \\\begin{bmatrix}0 & 0 & 0 & 0.4 & 1.6\end{bmatrix}\end{matrix}\quad\begin{matrix}\begin{bmatrix}1 & 1 & 0 & 0 & 0 & 0 & 0\end{bmatrix} \\\begin{bmatrix}0 & 1 & 1 & 0 & 0 & 0 & 0\end{bmatrix} \\\begin{bmatrix}0 & 0 & 1 & 1 & 1 & 0 & 0\end{bmatrix} \\\begin{bmatrix}0 & 0 & 0 & 0 & 1 & 1 & 0\end{bmatrix} \\\begin{bmatrix}0 & 0 & 0 & 0 & 0 & 1 & 1\end{bmatrix}\end{matrix}\begin{matrix}\left\lbrack {h\quad 1} \right\rbrack \\\left\lbrack {h\quad 2} \right\rbrack \\\left\lbrack {h\quad 3} \right\rbrack \\\left\lbrack {h\quad 4} \right\rbrack \\\left\lbrack {h\quad 5} \right\rbrack \\\left\lbrack {h\quad 6} \right\rbrack \\\left\lbrack {h\quad 7} \right\rbrack\end{matrix}$The matrix equation can be used to cancel intertrack interference. Theoutput of the matrix equation can be input to standard 1D channels. Alsonote that the offtrack signal can also be derived from a servo system,and can also be updated in a detector.

The invention can take the form of an entirely hardware embodiment, anentirely software embodiment or an embodiment containing both hardwareand software elements. In a preferred embodiment, the invention isimplemented in software, which includes but is not limited to firmware,resident software, microcode, etc.

Furthermore, the invention can take the form of a computer programproduct accessible from a computer-usable or computer-readable mediumproviding program code for use by or in connection with a computer orany instruction execution system. For the purposes of this description,a computer-usable or computer readable medium can be any apparatus thatcan contain, store, communicate, propagate, or transport the program foruse by or in connection with the instruction execution system,apparatus, or device.

The medium can be an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system (or apparatus or device) or apropagation medium. Examples of a computer-readable medium include asemiconductor or solid state memory, magnetic tape, a removable computerdiskette, a random access memory (RAM), a read-only memory (ROM), arigid magnetic disk and an optical disk. Current examples of opticaldisks include compact disk-read only memory (CD-ROM), compactdisk-read/write (CD-R/W) and DVD.

A data processing system suitable for storing and/or executing programcode will include at least one processor coupled directly or indirectlyto memory elements through a system bus. The memory elements can includelocal memory employed during actual execution of the program code, bulkstorage, and cache memories which provide temporary storage of at leastsome program code in order to reduce the number of times code must beretrieved from bulk storage during execution.

Input/output or I/O devices (including but not limited to keyboards,displays, pointing devices, etc.) can be coupled to the system eitherdirectly or through intervening I/O controllers.

Network adapters may also be coupled to the system to enable the dataprocessing system to become coupled to other data processing systems orremote printers or storage devices through intervening private or publicnetworks. Modems, cable modem and Ethernet cards are just a few of thecurrently available types of network adapters.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

1. A system for reading a magnetic medium having a data band thereon,the data band comprising a plurality of simultaneously written datatracks and at least one alignment band, the system comprising: aplurality of adjacent readers for simultaneously reading the data tracksand the at least one alignment band; a mechanism for determining afractional overlap of each reader on the data tracks based on readbackof the at least one alignment band; and a mechanism for extracting) datafrom readback of the data tracks based at least in part on thefractional overlap.
 2. A system as recited in claim 1, wherein thenumber of readers is at least equal to the number of written tracks inthe data band.
 3. A system as recited in claim 1, wherein two alignmentbands sandwich the data tracks, each alignment band including a blanktrick.
 4. A system as recited in claim 3, wherein the blank tracks areat least one of direct current (DC) erased tracks and alternatingcurrent (AC) erased tracks.
 5. A system as recited in claim 3, whereinone of the alignment bands includes first and second blank trackssandwiching a track with a predefined signal; wherein the otheralignment band is a third blank track.
 6. A system as recited in claim3, wherein each alignment band includes first and second blank trackssandwiching a track with a predefined signal.
 7. A system as recited inclaim 1, wherein a spacing between centerpoints of some of the readersis about equal to centerlines of the data tracks.
 8. A system as recitedin claim 1 wherein the data is extracted from the reader signals usingan inversion matrix.
 9. A system as recited in claim 8, wherein theinversion matrix is predefined except for the fractional overlap.
 10. Asystem as recited in claim 1, wherein the fractional overlap isdetermined from signals of at least two readers reading the alignmentband.
 11. A system as recited in claim 1, wherein the track alignmentsignal is present in a track with a known signal, wherein the knownsignal is a monotone pattern.
 12. A system as recited in claim 1,wherein the track alignment signal is further used to fine tunealignment of the readers with respect to the written tracks.
 13. Asystem as recited in claim 1, wherein the at least one alignment bandalso provides timing information for clock recovery.
 14. A system asrecited in claim 1, wherein the system is calibrated by performing amicrotrack profile calibration which includes shifting the readersperpendicularly with respect to the direction of media travel across thedata tracks.
 15. A system as recited in claim 1, further comprising: adrive mechanism for passing a magnetic recording tape over the readers.16. A method for reading a magnetic medium having a data band thereon,the data band comprising a plurality of simultaneously written tracks,the tracks including data and an alignment signal, the methodcomprising: receiving signals from a plurality of adjacent readerssimultaneously reading the data tracks; receiving a signal from at leastone reader reading the alignment signal; determining a fractionaloverlap of each reader relative to the data tracks based on the signalfrom the reader reading the alignment signal; and extracting data fromreadback of the data tracks based at least in part on the fractionaloverlap.
 17. A system for reading a magnetic medium having a data bandthereon the data band comprising a plurality of simultaneously writtendata tracks and at least one a alignment band, the system comprising: aplurality of adjacent readers for simultaneously reading the data tacksand at least one alignment band written simultaneously with the datatracks; a mechanism for determining a fractional overlap of the readerrelative to the data tracks based on readback of the alignment band; amechanism for extracting data from readback of the data tracks based atleast in part on the fractional overlap.
 18. A system as recited inclaim 17, wherein the data is extracted from the reader signals using aninversion matrix.
 19. A system as recited in claim 118, wherein theinversion matrix is predefined except for the fractional overlap.
 20. Acomputer program product, comprising: a computer usable medium includingcomputer usable program code for reading a magnetic medium having a databand thereon, said computer program product including: computer usableprogram code for receiving signals from a plurality of adjacent readerssimultaneously reading data tracks of the data band; computer usableprogram code for receiving a signal from at least one reader reading analignment signal of the data band; computer usable program code fordetermining a fractional overlap of each reader relative to the datatracks based on the signal from the reader reading the alignment signal;and computer usable program code for extracting data from readback ofthe data tracks based at least in part on the fractional overlap.